xr2 blown up

[blackbeard]

hi all,
i was out having a run on sunday,all going well until engine decided 2 shit its self and blow a big hole behind starter motor and bearings ect come trough reeds and carbs, waswondering if anyone could give me any advise why she blew, shes done no more then 10 hours since rebuild,was running 15psi water,32/1 rock oil mix and she was only reving 6500,
any advice will be much apreacated
chris

[still no worries]

check the carb on the piston that went.look for any crap in there (needle jet)
probably leaned out.

[lain]

It's a shame she went but hopefully this will be an interesting thread, I've always wondered why these motors are meant to be so temperamental. If you dont mind would you also take some pics of the bottom end when she's apart?

I've always heard that metal treatments can help prevent fatigue and failures and wondered if anyones tried this with these engines.

[The Docta]

Who rebuilt it / looks after it?

In my experience they are no more temperamental than any other engine (i owned on for several seasons without any major issues) but they are a race motor and do need to be looked after by someone who knows them well.

I think they get a bad press because they are often worked on by people who dont know them well and are badly rebuilt asa result.

Just IMHO but I would like to think that there are several class 3 / ex OCR A racers who would agree.

I think i saw that someone was advertising a couple of p'heads on the trading thread (pearney) at very reasonable prices.

Incidentally, i was advised to run mine on merc hi po semi synthetic and nothing else. Is the rock oil semi / fully sythetic

[blackbeard]

ive had a few xr2s one for 4 seasons with out any heavy maintance and run the shit out of it and never had any probs,imho i wouldnt say their that temperental,

rock oil is semi syn

when i bourt the powerhead it was a spare from a race team and was suppose to have been built by someone who knows xr2s and rebuilds them regualy,cant remeber who tho

the carbs seem to be clean(part from bits of engine in them)

going 2,5 efi now

[scooby_hugh]

If it was rebuilt a while ago it may have corroded abit on a bearing while it was sat which could have caused it to blow

[blackbeard]

Originally Posted by scooby_hugh

If it was rebuilt a while ago it may have corroded abit on a bearing while it was sat which could have caused it to blow

was sat for a couple of years, if this was the prob wouldnt it of let go before, have had 3 runs this season and quite a few last

[NIC SURRY]

Originally Posted by blackbeard

hi all,
i was out having a run on sunday,all going well until engine decided 2 shit its self and blow a big hole behind starter motor and bearings ect come trough reeds and carbs, waswondering if anyone could give me any advise why she blew, shes done no more then 10 hours since rebuild,was running 15psi water,32/1 rock oil mix and she was only reving 6500,
any advice will be much apreacated
chris

I've blown a few race engines and seen many blown customer engines in the past but not boat engines but the priciples are normally the same,If you can see any blueing of the con rod on the big end it could be lack of oil this results in bearing failiure allowing piston to touch the head and disintigtate into litle pieces so if this has happened you should see an impression in the carbon on the head.On a two stroke oil problems normally result in piston siezure which can then force the conrod out the side but normally leaves the piston in one piece or at least large pieces.or it could be just a con rod has let go-the pison could then be smashed to bits by the flailing conrod .It could be detonation problem that would burn a hole in the piston allowing bits to damage the big end bearings and throw a rod-the detonation can be caused by to much oil in the mix.I previusly had a big end failiure that allowed the piston to touch the head-when I removed the head there was no piston just a con rod and gudgeon pin rattleing arround in the bore,the biggest bit of piston I found was the size of a penny mostly it turned to dust.I'd be interested in your findings I hope this helps.Nic

[blackbeard]

[QUOTE=NIC SURRY;179570]I've blown a few race engines and seen many blown customer engines in the past but not boat engines but the priciples are normally the same,If you can see any blueing of the con rod on the big end it could be lack of oil this results in bearing failiure,,,,,,,,,,,,,,,,,,

thanks mate, il take heads off and post some pics,
piston is stil in 1 piece and moves freely through bore and by turning flywheel everything else moves freely

[sinkunit0]

rod bolt new or used on rebuild, correct torque?

[scooby_hugh]

Could also be metal fatigue in the rods or a material defect, how old is the motor?

[blackbeard]

dont know if new bolts were used, dont think i could find out,


the powerhead is 1999,

[Hydrostream]

Bearings came out the carbs sounds a little funny!
Rod bolts reused, not torqued down, not loctited. Rod caps upside down.

[Techteam]

Certainly looks rod related, If you look after an XR2 they are a really nice motor. I have several that regularly pull over 8800rpm with no problems.

[Jay Smith]

My guess is the engine was fitted with the stock OEM "El Cheapo" nylon caged con rod bearings, looking at the abrasion on the crank , I find them to be a high failure rate in engines recreational and fishing grade engines as well as Pro Max's . I NEVER rebuild ANY 2.5 with out up grading to the alum. caged High Performance con rod bearings...Also a use the Pro Marine rod bolts with Red Loctite applied and torque then once and if they are loosened or removed before running I throw it away and go back with new. I have tested the Pro Marine 5/16 th headed 12 point rod bolts against the OEM ones and found the Pro Marine rod bolts to yield a 10,000 stronger tensile strength that the OEM ones..But the SPS 3/8 headed High Performance rod bolt was 200,000 stronger than the fishing motor grade bolts and 10 times as expensive, the tests results were as followed:


1. OEM broke at 33,000 pounds Tensile Strength ( 5/16 12 PT. headed bolt )
2. Pro Marine broke at 43,000 pounds Tensile Strength ( 5/16 bolt )
3. SPS OEM HIGH PERFORMANCE broke at 243,000 Tensile ( 3/8 headed 12 point bolt )

Cheers,
Jay Smith

[NIC SURRY]

When I put a rod through the side of a 16 valve Astra engine on my Autograss car I set the car and the field on fire,!That was big end bolt failiure,Cheers Nic